Conventionally, an electrolysis of an alkali metal chloride solution, typically sodium chloride and potassium chloride solution, denoted also as brine, has been performed for the purpose of producing chlorine, sodium or potassium hydroxide, and hydrogen. Since the raw material in such processes usually contains alkali metal bromides as impurities, chlorine generated therefrom is contaminated with bromine. The bromine impurity in chlorine is less and less tolerated, especially in water treatment applications. This is because, in certain water treatment processes, bromine is at least partially converted to alkali metal bromate which is a known health hazard. Another application which requires chlorine with low bromine content is the production of various chlorinated organic compounds.
There are various approaches to dealing with the bromine contamination of the chlorine product. The first approach is to remove alkali metal bromide from the alkali metal chloride brine. Such an approach is described in numerous prior art documents, for example, U.S. Pat. Nos. 460,370, 2,622,966, 3,371,998, 5,069,884, and 6,428,677, British Patents Nos. 382,512, 526,542, 893,692, and 991,610 and Modern Chlor-Alkali Technology, Volume 7, pp. 157-159, published in 1997.
Another approach is based on the purification of chlorine product, typically by distillation (see, for example, WO 2004/018355) or another process (see European Patent No. 979,671 or US Patent Application No. 2008/0224094).
Yet another approach, described in the U.S. Pat. No. 3,660,261 and WO 2005/068686, involves an oxidation of various bromine species present in brine to alkali metal bromate, which is claimed to result in the production of chlorine with low bromine content.
All the above-described processes are very costly and, in some cases, for example distillation, also energy intensive. There is, therefore, a need to develop a relatively simple and inexpensive process which results in the production of chlorine with low bromine content.